The present invention relates to a steam trap for automatically discharging condensate generated in various kinds of steam using equipment and steam pipe lines, and, more particularly, to a thermally-actuated steam trap adapted to discharge the condensate below a desired temperature out of a system by using a temperature control element including a medium which is heated and expanded by steam and cooled and contracted by condensate.
Such a thermally-actuated steam trap is provided with a body having therein a valve chest in which steam or condensate is introduced and a temperature control element disposed in the valve chest. The temperature control element used for such a steam trap comprises two disk-like wall members, an upper one and a lower one, and at least one diaphragm provided between the two wall members, the diaphragm being secured at its outer peripheral edge to both the wall members, and the inner space formed between the upper wall member and diaphragm accomodating an expansible medium which changes in volume corresponding to the temperature. Further, on the diaphragm at the side opposite the expansible medium side is carried a valve member.
In such a steam trap, since the diaphragm member and the valve member are displaced to perform the opening and closing operations of the valve part, the diaphragm member composed of a particularly thin member is often damaged and the steam trap comes not to fulfill its function; so, it has hitherto been widely performed to constitute the diaphragm member with a plurality of diaphragm sheets for its reinforcement, as shown in DE 26 30 038 B1. U.S. Pat. No. 4,955,536 also shows a plurality of diaphragms in its drawings without depending upon their relation to the technical contents proposed therein. Further, there are also known steam traps provided with a plurality of diaphragms in such a state as shown in U.S. Pat. No. 4,013,220 and EP-A-0012267.
Moreover, the inventor of the present application filed a thermally-actuated steam trap, which permits condensate to also be discharged when the diaphragm member is damaged, as in U.S. Pat. application Ser. No. 07/851,388, European Pat. Application No. 92104066.3, Canadian Pat. Application No. 2,062,930-1, Australian Pat. Application No. 12182/92, and South African Pat. Application No. 92/1879, and took out patents for the invention (U.S. Pat. No. 5,191,669, Australia Pat. No. 638184 and South African Pat. No. 92/1879). This invention comprises a temperature control element in which an expansible medium is sealed in an accommodating chamber between an upper wall member and a first diaphragm, a valve member is connected to a second diaphragm member, and the second diaphragm and the valve member are each formed with a through-hole.
In the thermally-actuated steam trap provided with the plurality of diaphragms as described above, an inflow of steam at a high temperature into the valve chest causes the expansible medium to expand, thereby displacing each diaphragm in the direction of closing the valve, so that the valve member carried by the lower diaphragm (second diaphragm) or the diaphragm per se is brought into a seating engagement with the valve seat member and, accordingly, the discharge passage formed on the valve seat member is closed. This prevents the discharge of steam. On the other hand, an inflow of condensate at a low temperature in the valve chest causes the expansible medium to contract, thereby displacing each diaphragm in the direction of opening the valve, so that the valve member or the diaphragm per se is brought out of a seating engagement with the valve seat member to open the discharge passage, thereby discharging the condensate out of the system.
However, the thermally-actuated steam trap as constructed above has a problem in that, in the case where the fluid at the inlet side has no sufficient pressure, the discharge passage can not be opened. Namely, when the expansible medium contracts, the chamber in which the expansible medium is accommodated comes to be in a state of negative pressure, so that the upper diaphragm (first diaphragm) is displaced in the direction of opening the valve; however, with the fluid at the inlet side being weak in pressure, the lower diaphragm, particularly fitted with the valve member, can not follow the upper diaphragm, that is, it can not be displaced in the direction of opening the valve, and accordingly, the valve member is not brought out of a seating engagement with the valve seat member, so the discharge opening can not be opened. For example, in a steam-using equipment or the like, the pressure and temperature in the system are low at an initial stage of transferring steam, and the upper diaphragm is displaced in the direction of opening the valve; however, the lower diaphragm remains in the position of closing the valve and, therefore, condensate can not rapidly be discharged and a considerable amount of condensate accumulates in the steam trap, resulting in a lowered machine efficiency.
Moreover, in the thermally-actuated steam trap provided with the plurality of diaphragms, the construction in which the plurality of diaphragms are connected to the valve member so as to be able to be integrally moved therewith or the construction in which the lower diaphragm is combined with the function of the valve member causes the diaphragm to be fractionally displaced due to a change in temperature, in the case where the expansible medium has a temperature close to the temperature at which the opening and closing operations of the valve are switched, so that the opening and closing operations of the valve are finely repeated as if it were vibrated, thus having the danger of such operations being mistaken for a leakage of steam. Further, such fractional displacements cause the earlier abrasion of the valve part, resulting in a leakage of steam.